An electrochemical method has been developed for catecholamine analysis in vivo at specific locations in the brain. This method, differential double pulse voltammetry (DDPV), is based upon comparison of the current which flows when two unequal square wave potential-pulses are applied to the indicator electrode. DDPV has been successfully applied to the adult, male Sprague-Dawley albino rat in basic work leading to this proposal. Electrochemical methods in general offer the advantage that they perform analyses: (1) in vivo; (2) instantaneously; (3) localized to a small region of the sample; (4) non-destructively and repetitively; (5) selectively in the liquid phase; and (6) quantitatively. DPPV, in particular, offers additional advantages: (7) efficient exclusion of normal background interference; (8) long-term electrode stability; and (9) optimal resolution of overlapping peaks. The indicator, a Pt microelectrode, can be modified chemically, leading to a superior stability, accuracy and selectivity. It is proposed to continue these studies in order to optimize: (a) electrode characteristics and (b) the measuring technique by further testing and exploration of designs, coatings and procedures; (c) quantitatively explore the influence of brain matter heterogeneity on electrode response; (d) determine catecholamine levels vs. position in the brain; and (e) vs. drug administration and electrical stimulation.